617.7  Unknown defendants.
  Where it is necessary to make an unknown person defendant, the petition shall be sworn to and state the claim of plaintiff with reference to the property involved in the action, that the name and residence of such person is unknown to the plaintiff, and that the plaintiff has sought diligently to learn the same.
[R60, §2836; C73, §2622; C97, §3538; SS15, §3538; C24, 27, 31, 35, 39, §11082; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §617.7]